Telephone service to the home has been provided by aerial or buried service wire. Typically each of these has included a pair of metallic conductors such as cooper wires enclosed in a jacket. For purposes of self-support, the aerial wire also has included at least one strength member.
The use of optical fibers in communications has grown significantly over the past few years. It is anticipated that its use will reach into the residential loop distribution system in the near future. For now, loop distribution cables which include insulated metallic conductors continue to be installed.
Nevertheless, operating telephone companies have expressed a desire to install cables which include optical fibers as well as metallic conductors. Such a course of action of early placement of optical fibers in aerial or buried installations to customers' premises will facilitate the later transition from a metallic to an optical fiber operating system. Obviously, the first cost of installing optical fiber to customers' premises is minimized by such an approach. With such a cable, optical fiber can be provided to customers' premises awaiting the arrival of the optical fiber network and development of associated hardware and electronics.
Such composite cables will be placed by the same methods and apparatus as are used for all-copper cables. Accordingly, the optical fiber portion thereof must be robust enough to withstand plowing and trenching or aerial stringing of a host structure and to be capable of survival outside the host structure in a separate run to an optical fiber storage or termination point.
With such a cable structure in place, service will evolve from the metallic pairs to the optical fibers. Simple telephone service can begin immediately over a metallic pair of conductors. Other metallic conductor pairs of the distribution and service cable can serve as secondary lines or alarm circuits. Initially, the optical fiber unit may be used to provide cable television or retained for later use.
At a later date, more sophisticated offerings which require increased bandwidth and customer interaction such as, for example, electronic newspapers and mail, catalogs and shopping, banking and business activities and data and computer functions may be served through a remote terminal. For this application, metallic conductor pairs may provide power to on-premise electronics or serve as control circuits. Still later, all offerings may be provided over the optical fiber media, but power still will have to be provided for on-site electronics by the power or telephone operating company. Providing power from a central office source through these structures should result in reliable telecommunications during power outages. Also, the copper conductor pairs may have other uses such as circuit maintenance, for example.
The sought-after cable should have desired properties. For example, it should have a relatively high tensile and compressive axial loading capability, a relatively low minimum bend radius, stiffness against bend losses in order to insure that the optical fiber unit does not follow the twists and turns of neighboring twisted pairs and should remain as straight as possible to minimize bend losses, an operating temperature range of about -40.degree. to +160.degree. F., single mode capability and low cost. The cable should be properly cushioned to withstand repeated impacts by vehicles on structures routed across roadways during installation. Also, the structure must not be affected adversely by cable filling compounds. The cable must be water-resistant to prevent damage due to water-induced crack propagation or freezing. Inasmuch as in some instances it will connect to customers' premises, the cable must be capable of being made flame retardant.
Seemingly, the prior art is devoid of such a cable which provides both metallic and optical fiber conductors along with the desired properties. Single optical fiber cables having an optical fiber and strength member yarn disposed between the optical fiber and a plastic jacket are available commercially. However, such a cable does not provide columnar strength in compression and is not suitable for outside plant, particularly at relatively low temperatures. The sought-after cable will fill a need in the marketplace as services to the home are expanded.